One of the problems faced by the perfumery industry lies in the relatively rapid loss of the olfactive benefit provided by odoriferous compounds due to their volatility, particularly that of “top-notes”. This problem is generally tackled using a delivery system, e.g. capsules containing a perfume, to release the fragrance in a controlled manner.
Polyurea capsules, formed by polymerisation between a polyisocyanate and a polyamine, are well known capsules that are used in a large variety of technical fields, including perfumery. However, such delivery systems may suffer from stability problems when incorporated into surfactant based products such as detergents or fabric-softeners, which are strongly aggressive towards said delivery systems.
It is especially difficult to prepare capsules having both good stability and good olfactive performance. The perfume retention ability, and therefore the ability of the capsules to avoid loss of the volatile ingredients, is in particular dependent on the stability of the capsules in the product base. On the other hand, the hedonic effect perceived by the consumer using a perfumed product, and therefore its perception of the quality of such a product, depends on the olfactive performance of the capsules. In particular, capsules having a good stability in a product base do not automatically have good olfactive performance. It is therefore desirable to provide capsules having both good stability and good olfactive performance.
Several prior art documents address the problem of the stability of polyurea microcapsules.
This is for example the case of U.S. Pat. No. 3,886,085, which discloses a process for the preparation of microcapsules of fine oil droplets employing a polyisocyanate adduct having a free isocyanate group and a polyamine or a polyamine adduct having a free amino group. Among the polyisocyanate adducts that can be used, aromatic ones are mentioned. Such a process allegedly produces capsules encapsulating a perfume, wherein the perfume can be preserved for a long period of time without being released through the capsule walls or shells (i.e. stable capsules). However, the capsules are specifically designed to be applied on paper. It is well known that the presence of surfactants in perfumed products such as home- and personal-care products renders these product bases very aggressive to capsules incorporated therein, thus having a very negative impact on the storage stability of the capsules. Such aggressive conditions do not exist when the capsules are applied on paper, so that stability of capsules applied on paper cannot be compared to stability of microcapsules in surfactant-containing mediums, such as perfumed products. Moreover, the problem of the capsules olfactive performance is not addressed in this document.
U.S. Pat. No. 4,668,580 describes a process for the production of polyurea microcapsules, in which a large variety of polyisocyanates can be used including aliphatic and aromatic ones. Example 3 of this document uses a mixture of polyisocyanate consisting of 90% biuretized hexamethylene-diisocyanate and 10% carbodiimide-modified polymethylenepolyphenyldiisocyanate. This document addresses the problem of providing capsules having an “inhomogeneous” organic phase having an organic liquid and a polyisocyanate insoluble therein. The application of this technology in the field of perfumery is not envisaged or even suggested in this document. Therefore, the problem of combining both storage stability of perfume capsules and good olfactive performance is not addressed in this document.
The present invention provides a new process for the preparation of polyurea microcapsules. It advantageously solves the problem of providing highly stable capsules having at the same time good olfactive performance. The present solution to this problem is not described or even suggested in any prior art document.